Rather, this solar energy warms the Earth, and the Earth emits its own energy to space. Because the surface of the Earth is much cooler than the surface of the Sun, the Earth emits most of its energy at longer wavelengths.

As a form of energy heat has the unit joule (J) in the International System of Units (SI). However, in many applied fields in engineering the British thermal unit (BTU) and the calorie are often used. The standard unit for the rate of heat transferred is the watt (W), defined as joules per second.

Heat is measured in many different ways, in different countries. From more scientific accurate ways, to more simple ways. Kelvin, which is used to precisely measure temperatures from zero degrees, which at that point would be absolute zero. Celsius and Fahrenheit, are more simple, easy to calculate ways to measure temperature, as most of us do not experience negative degrees on a daily basis, or extremely high temperatures on a daily basis. British thermal units are more versatile than all of these, with the measurement of a single degree allowing one pound of water to be heated up one degree Fahrenheit.

As a form of energy, heat has the unit joule (J) in the International System of Units (SI). However, in many applied fields in engineering the British thermal unit (BTU) and the calorie are often used.